Because of the dusty environment in which machines such as harvesters operate, it is important to filter the air passing through the radiator of the engine cooling system and any heat exchanger of an air conditioning or hydraulic system. As the filter itself can become blocked, it is common to pass the cooling air through a self-cleaning rotary filter screen. Such screens are known which rely on two mechanisms in order to remain clean. First, the rotation of the screen dislodges filtered particles. Second, a plenum chamber under low pressure is provided at a point around the circumference of the screen which acts as a vacuum cleaner to suck dust off the screen as it rotates.
Despite these measures, some crops generate a sticky mist during harvesting which causes the rotary screen to clog. On occasions the clogging is so severe that no air can pass through the filter screen, which then results in overheating of the engine. This necessitates cleaning of the rotary screen by the machine operator and such cleaning may be needed several times a day. However, the equipment needed for cleaning the rotary filter screen, such as a hard brush, a power washer and/or an air compressor, may not always be available to the machine operator. Furthermore, the prevailing conditions, such as low light or poor weather, may hinder the operator from performing the task of unclogging the rotary screen filter. Even under good conditions, an operator will not wish to leave a comfortable cab to undertake such a dirty and unpleasant task.
A rotary screen consisting of a perforated cylindrical drum can be cleaned using a cylindrical brush which is placed within the filter screen and is moved radially by an actuator such as a solenoid to engage in the perforations. Such systems have been in use for several years on combine harvesters manufactured by the present. Applicants intended for harvesting corn.
Rotary filter screens which employ a perforated disc in place of a drum run at higher speeds (typically 150 to 300 rpm) and cannot be cleaned easily with brushes because the speed gradient from the centre towards the outside diameter causes irregular wear of the rotary brush. A rotary brush can be made in different sections rotating at different speeds to reduce the slippage but this in itself creates other problems. Furthermore, there is often insufficient space to accommodate such a row of brushes and their actuation system on the inside of the screen.